Memory devices, such as Dynamic Random Access Memory (DRAM), utilize capacitors to store information within an integrated circuit. A capacitor is formed by placing a dielectric material between two electrodes formed from conductive materials. A continuing goal for memory devices is to decrease the dimensions of the devices while maintaining or increasing the storage capacity of the devices.
Capacitance (C) is an ability of a capacitor to hold electrical charge. Capacitance (C) is a function of the surface area of the capacitor (A), the distance between the capacitors (d) (i.e., the physical thickness of the dielectric material), and the relative dielectric constant (i.e., k value) of the dielectric material, as shown in the equation below where ∈o represents the vacuum permittivity:
  C  =      k    ⁢                  ⁢                  ɛ        o            ·              A        d            
In order to enhance a capacitance value without increasing the dimensions (e.g., area A) of an electrode, it is necessary to decrease the thickness (d) of the dielectric material or to use a dielectric material having a high dielectric constant (k). Reducing the thickness (d) of the dielectric material may result in current leakage, which exponentially increases as the thickness of the dielectric material decreases. It is, therefore, desirable to use a dielectric material with a high k value to achieve high capacitance.
For a given desired capacitance, if the k value of the dielectric material is increased, the dimensions of the capacitor may be decreased while maintaining the same cell capacitance. High-K dielectric materials are dielectric materials having a high dielectric constant (k) of about 20, as compared to silicon dioxide (SiO2), which has a dielectric constant of about 4. Therefore, a capacitor with the same or increased capacitance can be obtained by using a high-K dielectric material, instead of SiO2, as the dielectric material between the two electrodes of the capacitor. Examples of high-K dielectric materials are zirconium dioxide (ZrO2), hafnium dioxide (HfO2), SrTiO3, hafnium silicate or zirconium silicate, among others.
However, high-K dielectric materials also have smaller band gaps and smaller conduction band offsets with respect to the metal electrode, compared to SiO2. Consequentially, the capacitors having high-K dielectric materials typically suffer from current leakage more than the capacitors having SiO2 as a dielectric material.
Accordingly, there is a need for an electrode and a semiconductor structure including such electrode that have high capacitance and work function, but low current leakage.